A dual homing technology in Next Generation Network (NGN) field can prevent a soft switch from paralyzing or provide disaster tolerance mechanism of emergent communication when a burst disaster appears in a system. In the case of extreme exceptions, when the system enables dual homing control mechanism, 80%˜90% of the communication capability should be able to be restored.
FIG. 1 is a schematic diagram illustrating dual homing control technology:
The service management layer includes: service management devices, such as a Network Management System (NMS) a Media Resource Sever (MRS) and a Service Control Point (SCP) etc; these service management devices are connected with lower layer gateway devices via soft switches. Soft switches A and B have the mutual aid function, i.e., when the soft switch A (B) is in failure or the communication is interrupted, the soft switch B (A) can take over part or all of the services of the soft switch A (B); there is a heartbeat link (which adopts private protocol, and is indicated by a bold real line in FIG. 1) between soft switches A and B, which is used to detect mutually whether the operation of the opposite soft switch is normal. The soft switches A and B can be located physically in different geographical areas, and can be regarded as two independent exchanges in terms of networking.
The soft switches are connected with gateway devices of access point A and access point B via IP packet network or Public Switched Telephone Network (PSTN). The solid lines denote primary signaling channels, and dashed lines denote secondary signaling channels. The gateway devices include: an Integrated Access Device (LAD), an access media gateway, a universal media gateway, a trunk media gateway and a packet terminal etc; the packet terminal includes a H.323 terminal or a SIP terminal. These terminals can be hard terminals or soft terminals.
The dual homing control technology mainly consists of two parts, one is dual homing mechanism controlled by gateways, and another is dual homing mechanism controlled by services. In the dual homing controlled by gateways, each soft switch is configured with both the data of gateway devices controlled primarily by the soft switch and the data of gateway devices controlled secondarily by the soft switch, and each gateway device or packet terminal is configured with the related information of its primary homing soft switch and secondary homing soft switch, consequently, when one of the soft switches doesn't work or performs the dual homing handover, the gateway device which is controlled primarily by the soft switch can re-register to the secondary homing soft switch automatically or under the instruction of the secondary homing soft switch.
In the dual homing controlled by services, the user data and the office data, such as the local number-header set, the call source code, charging source code, the user number segment, the route number, the route selection code, the trunk group number, the call prefix etc., are planed uniformly between the soft switches A and B, so that both of the two soft switches can take over part or all services of the opposite soft switch when the dual homing handover happens, and all the attributes of the users, such as call and charging attributes, will not be affected before and after the handover. The system is configured with unified network management for centralized management of all the elements in the network, so as to guarantee that the office data or user data of the two soft switches can remain consistent or coordinated When the dual homing solution is adopted in networking, the amount of gateways and users that can be controlled by a single soft switching office is proposed not to exceed 50% of the rated capability of the soft switch.
The dual homing handover means a process, in which, when a soft switch is in the mutual aid work mode, the mutual aid state of the soft switch is converted from an inactive state into an active state, or the active state is restored into the inactive state. The active state means that a soft switch has taken over the service control of its mutual aid soft switch; and the inactive state means that a soft switch has not taken over the service control of its mutual aid soft switch. The way of handover may include manual mode and automatic mode:
The manual handover mode: when a soft switch is in the mutual aid work mode, the mutual aid state of the soft switch will change only after an operator sends the handover instruction to it via a terminal system or a network management system; the automatic handover mode: when a soft switch is in the mutual aid work mode, the soft switch will determine automatically whether the mutual aid state needs to be changed according to the state of the heartbeat link between the soft switch and its mutual aid soft switch.
The heartbeat signal exists between two mutual aid soft switches, which is a detection mechanism implemented by the local soft switch to determine the work state of the opposite soft switch. If the local soft switch hasn't received the heartbeat signal transmitted by the opposite soft switch within a scheduled time, the local soft switch may consider that the opposite soft switch is subject to the failure. Then the mutual aid state of the local soft switch will change from the inactive state to the active state if the local soft switch is in the automatic handover mode.
The gateway device determines the work state of the soft switch by the handshake signal between the soft switch and the gateway device. If the gateway device hasn't received the handshake signal transmitted by the soft switch within a scheduled time, the gateway device may consider that the soft switch that controls it (the primary homing soft switch) is subject to the failure. Thus, the gateway device will request for registration at another soft switch (the secondary homing soft switch).
in addition, in order to have cooperation between the soft switch and the gateway device, it's necessary to use a timer. The duration of the heartbeat signal detection timer (generally 1˜5 minutes) of the soft switch should be generally shorter than that of the handshake signal transmission timer (generally 5 minutes), i.e., only after the local soft switch has detected that the transmission of the heartbeat signal from the opposite soft switch is overtime, the local soft switch can normally process the registration application transmitted by the gateway device which is secondarily-controlled by it; if the local soft switch has received the registration application of the gateway device secondarily-controlled by it before it detects that the transmission of the heartbeat signal from the opposite soft switch is overtime, the local soft switch will reject the registration application of the gateway device secondarily-controlled by it.
Although the dual homing mechanism of the NGN has been realized in the prior art, some new problems appeared with the increase of requirement of the NGN broadband services-Broadband services have strong requirements for bearer network (such as enterprise network and premise network) in IP address translation, Quality of Service (QoS) guarantee, security guarantee, etc., however, the media streams can not pass through the Network Address Translation (NAT) device and the firewall device in the NGN itself In order to solve these problems, it's necessary to add a Session Border Controller (SBC) to the edge of the present IP network to constitute a services-based intelligent network, so as to realize passage of the media stream through the NAT device and the firewall.
SBC can be regarded as an agent supporting the VoIP (Voice over IP), which is a device that can identify the application layer and identify the information of the fifth layer and the seventh layer, and also can process various session signaling protocols of the fifth layer and modify the address of data packet header, so as to realize the address translation between the inner and outer network of the SBC. Meanwhile, the SBC can assist the VoIP to pass through remote firewall or the NAT device. Generally, SBC may be set on the network core switch side, and after coordination and modification, all of the signalings and media streams that pass though the SBC can be transmitted correctly on the system side and user side, and the NAT or firewall on user side may accept the modified signalings and media streams and transmit them to the inner network on user side.
SBC can assist the Session InitiationProtocol (SIP)/Media Gateway Control Protocol (MGCP) signaling to pass through the existing firewall or NAT, and the existing firewall or NAT device doesn't need to be changed. Particularly, for SIP terminal, the SIP terminal device will send the registration message periodically to SBC; for MGCP terminal, when the first registration message of the MGCP device has been received, SBC will send the Audit Endpoint (AUTEP) message to terminal periodically and force the terminal to continually reply with the 200 OK message periodically. Thus, because signaling messages pass through the firewall or NAT device continually, a fixed port may be maintained for the passed message stream by the firewall or NAT device; in addition, when the registration messages pass through the SBC, the information, such as the ports and the IP address of the third layer of the firewall, will be recorded, and this information will be recorded together with the information of the fifth layer, such as the username or telephone number of the terminal behind the firewall. Thus when a signaling arrives, SBC will send it to the called party with the correct address and port of the firewall.
When the call has been established, the bi-directional ports for media stream are established dynamically. Since the media stream will also pass through the SBC, the IP address and the port of the firewall can be identified by SBC according to the call related to the media stream (the username or the telephone number of the information of the fifth layer). Therefore, the corresponding media stream can be sent to the related IP address and port of the firewall by the SBC and then reaches the user side behind the firewall correctly.
Although the transmission of the media stream through the NAT and the firewall may be realized in the foregoing services-based intelligent network constituted by SBC, the dual homing mechanism can not be implemented as in the present NGN network, so the paralysis of the soft switch can not be prevented, and the disaster tolerance mechanism of emergent communication can not be provided when a burst disaster appears in the system.